An exhaust system connected to an internal combustion engine or other combustion engine of an automotive vehicle to discharge an exhaust emission is an example of a fluid transporting system which includes hollow products and through which the exhaust emission that is a fluid is transported or discharged. For instance, the exhaust system includes hollow products such as an exhaust manifold 1, a catalytic converter 2, a pipe 3, a pre-muffler 4 and a main muffler 5, as shown in FIG. 15. The catalytic converter 2 is arranged to induce chemical reactions such as oxidization and reduction for purifying the exhaust emission produced by the combustion engine and received through the exhaust manifold. The pre-muffler 4 and main muffler 5 are arranged to reduce a noise of the exhaust emission as discharged into the atmosphere, by lowering the pressure of the high-pressure exhaust emission as received through the catalytic converter 2 and the pipe 3.
Each of the hollow products such as the exhaust manifold 1, catalytic convert 2, pipe 3, pre-muffler 4 and main muffler 5 is generally a unit assembly consisting of a hollow member 100 such a container or a connector pipe, and other members in the form of flange members 110 connected to joining portions 100b of the hollow member 100, as shown in FIG. 16 (in which only one joining portion 100b and only one flange member 110 are shown). For easy assembling of the hollow products or for easy replacement of a damaged one of the joined hollow products, the adjacent hollow products are removably joined together with bolts at the flange members 110.
JP-A-9-324623 discloses an example of a known technique for manufacturing a hollow product consisting of the hollow member 100 such as a connector pipe and other members in the form of the flange members 110. This technique employs butt friction welding for joining together the hollow member 100 and the flange member 100.
JP-A-7-144287 discloses a friction welding apparatus which includes a deburring rod for removing burrs produced inside the hollow member during the friction welding to joint the hollow member and the other member together. The deburring rod is arranged to press down the produced burrs onto the inner surface of the hollow member.
JP-A-52-75641 discloses a friction-welding and fitting method of friction-welding a first member having a circular hole and a second member having an outside diameter considerably larger than the diameter of the circular hole, in which the second member disposed coaxially with the circular hole is press-fitted into the circular hole while the first and second members are rotated relatively to each other about the common axis.
JP-A-55-61389 discloses a method of friction-welding together a tubular roller body, and a journal which has a tapered portion, a shaft portion extending from the large-diameter end face of the tapered portion and a circumferentially grooved portion and a baffle plate portion which are formed on the small-diameter end face of the tapered portion. The baffle plate portion has a diameter substantially equal to an inside diameter of the tubular roller body. In the friction welding, the journal is press-fitted into the roller body by pressing the baffle plate portion onto one end of the roller body, for friction welding of the journal at the outer circumferential surface of the tapered portion to the roller body, such that burrs produced within the roller body are accommodated in the circumferentially grooved portion.
However, the butt friction welding of the two hollow members 100, 100 to form a hollow product as disclosed in JP-A-9-324623 suffers from burrs produced outside and inside the butt-welded portion, as shown in FIG. 17. Where the hollow product thus manufactured is used as a part of a fluid transporting system, there are drawbacks due to the burrs. Namely, the burrs inside the hollow product lower the efficiency of flow or transportation of the fluid such as an exhaust emission through the fluid transporting system, and the burrs outside the hollow product deteriorates the appearance of the hollow product. Where the deburring rod as disclosed in JP-A-7-144287 is used to remove the burrs produced inside the hollow product, the friction welding apparatus is undesirably large-sized, and the cost of manufacture of the apparatus is increased.
The method of press-fitting the second member into the first member by friction welding as disclosed in JP-A-52-75641 requires the inside diameter of the circular hole of the first member to be made larger than the outside diameter of the second member to effect the friction welding, so that a pressure between the circular hole of the first member and the outer circumferential surface of the second member cannot be directly controlled. Further, this method does not permit application of an upsetting pressure in the final stage of the friction welding process. Where the second member is a hollow member such as a pipe, the pressure acting on the hollow member in the radial direction cannot be controlled due to deflection of the hollow member during the press-fitting of the hollow member into the first member, resulting in problems such as a shortage of the amount of heat generated due to the friction between the first and second members, and a shortage of the friction welding force in the radial direction.
The butt friction welding method disclosed in JP-A-55-61389 requires the journal to have the tapered portion, circumferentially grooved portion and the baffle plate portion, resulting in a problem of inefficient manufacture of the journal. Further, the baffle plate portion which is inserted into the tubular or hollow roller body is required to have a diameter not larger than the inside diameter of the roller body, so that there is a risk that the burrs produced inside the roller body during friction welding of the journal within the roller body more or less flow out from the grooved portion, over periphery of the baffle plate portion. Further, the present method in which the tapered portion of the journal is friction-welded to the roller body requires the tapered portion to be formed with a high degree of accuracy of its taper angle. In addition, a relative movement of the tapered portion and the roller body in their axial direction has a large influence on the friction welding force in the radial direction, so that it is difficult to control the friction welding force.